The use of hydrophilic polyisocyanate crosslinkers in the leather, adhesives, paints and varnishes fields has been known for a long time.
Generally, emulsifiable or water dispersible polyisocyanate compositions are co-formulated shortly before use with other products, mainly with aqueous polyurethane or polyacrylate aqueous dispersions and/or emulsions, and applied on the item which is to be treated.
Emulsifiable polyisocyanates, in fact, react by means of their isocyanate groups with the active hydrogens of the polymers and eventually of the item itself, thus generating a crosslinking which renders the film highly resistant.
Many patents describe the preparation and use of water dispersible polyisocyanates which are useful as crosslinkers.
By way of example, U.S. Pat. No. 4,663,377 describes water dispersible polyisocyanate compositions comprising a water emulsifiable polyisocyanate obtained from the reaction of an aliphatic polyisocyanate with a nonionic polyether alcohol containing oxyethylene units; U.S. Pat. No. 4,663,377 does not describe the use of 1,3- or 1,2-nonionic diol containing one alkoxy-terminated polyoxyethylene chain as the polyether alcohol.
U.S. Pat. No. 5,583,176 refers to water-emulsifiable polyisocyanates obtained from the reaction of polyisocyanates with compounds containing a sulphonic group (or anion thereof) and a functional group capable of reacting with the isocyanate groups; among these compounds the use of a 1,3-sulphonated diol containing one oxyethylene chain is cited, but without attributing to it particular advantages.
U.S. Pat. No. 5,852,111 describes polyisocyanate compositions comprising hydrophilic polyisocyanates and an ionic surfactant; in the patent only ionic surfactants in the form of salts are used; non ionized surfactants in acid form are never discussed.
In our patent application EP 1 567 574 stable aqueous dispersions of blocked polyisocyanates are described which have been obtained from the reaction of a polyisocyanate, a blocking agent and 1,3- or 1,2-nonionic diols, together with their use in the preparation of textile finishing agents.
The scope of the present invention is to provide non aqueous stable compositions comprising non-blocked nonionic hydrophilic polyisocyanates useful as crosslinkers for water dispersed polymers, particularly for polyurethanes, and capable of forming films having high mechanical and chemical resistance, good adhesion especially on leather and skins, together with high transparency.
It is a further object of the present invention to provide compositions comprising non-blocked non-ionic hydrophilic polyisocyanates which are readily dispersible in water and are as stable as it is adequate for industrial use.